On today's construction sites superplasticizers find wide spread use for improving concrete. In modern constructions in housing or civil engineering, which are heavy reinforced, prestressed or require high final strength and durability, concrete coming from ready mix plants or concrete which is mixed on job sites must fulfill sometimes extraordinary high requirements regarding water reduction, workability, compactation, durability and strength.
In former years, water reducers from mid to high range based on lignin, naphthalene sulfonic acid condensates, melamine formaldehyde condensates or copolymers based on maleic acids found intensive use. These water reducers were useful to reduce water content of fresh concrete and, thus, to enhance workability, fluidity (“slump”), durability and strength.
However, as from construction site the standards regarding properties of fresh and/or hardened concrete became more and more sophisticated, this kind of polymers were inappropriate if high water reduction was required, because this could only be achieved by adding high dosages of water reducer, which, however, led to undesired effects like strong retardation, stiffening and dramatically loss of fluidity (called “slump loss”).
In recent years, a new kind of superplasticizers based on poly(acrylic acid) and polyethyleneglycol came up. Said superplasticizers were no longer linear polyelectrolyts but showed a comb like structure. Superplasticizers with this new structure caused a higher water reduction than the water reducers used before and were accompanied by a much lower retardation. Thus, this kind of new polymers was useful for modern construction sites with high standards because low dosages could be used with improved workability of fresh concrete and improved durability and final strength of hardened concrete.
Dispersants with the above mentioned features, obtained by copolymerizing (meth)acrylic acid or a salt thereof with (alkoxy)polyalkylene glycol mono(meth)acrylic ester are e.g. disclosed in EP 0 753 488.
Polymeric additives imparting to the wet cement composition the above mentioned advantages, and in addition comprising air detraining functional side chains, are disclosed in WO 97/00898.
However, despite of the improvement regarding water reduction and slump loss, it is still a challenge to fit to the various requirements coming form construction sites worldwide. This is due to different climates, cements, aggregates, cement replacing fillers etc., but also due to a wide spread application field like precast, ready mix, self compacting concrete, shotcrete, on site concrete etc., where the admixtures are faced some times with completely different demands.
Hence, to fit every request coming from construction sites, it is often necessary to use blends of polymers as water reducing admixtures. Consequently, a pool of differently performing polymers, i.e. polymers with high or moderate water reduction, with constant or increasing slump flow, with more or less retardation, or polymers with special features like set accelerating, and/or corrosion inhibiting must be available.
The polymer analogous reaction of carboxylic groups containing polymers with polyalkyleneglycol-monoalkylether, α-amino-polyalkyleneglycol-ω-alkylether or other amines is described in U.S. Pat. No. 5,728,207, U.S. Pat. No. 5,840,114 and WO-A-98/31643. However, the polymers disclosed in the above mentioned state of the art documents do not fit all various requests coming from construction sites worldwide.
Thus, it is desirable to provide improved polymers that are obtainable by an easy and convenient synthesis method, as well as such a method which gives the feasibility to establish a pool of differently performing polymers based on few raw materials and only one synthetical approach, but with different properties like high water reduction, constant slump flow or increasing slump flow.